Allocation of signal-to-noise ratio margin in multi-carrier systems

ABSTRACT

Allocation of different signal-to-noise margins to different carriers in a multi-carrier system is described. A preferred embodiment comprises assigning signal-to-noise ratio (SNR) margins to carriers in a multi-carrier system, comprises assigning a first SNR margin to a first data service based upon a first service characteristic, assigning a second SNR margin to a second data service based upon a second service characteristic, transmitting data associated with the first data service using the first signal-to-noise margin, and transmitting data associated with the second data service using the second signal-to-noise margin.

BACKGROUND

In a digital communication system, digital data is converted to analogsignals by modulating the data onto a carrier. The modulated carrier isthen transmitted over a physical medium, such as copper wires or awireless radio frequency (RF) connection. The physical medium may bedivided into bands, wherein each band is assigned to one or morecarriers, tones, or sub-carriers. The amount of data that is allocatedto a specific bandwidth depends upon the ratio between the signal powerassociated with the carrier and the noise power in that band. Thisparameter is referred to as Signal-to-Noise Ratio (SNR).

In order to achieve good performance in channels with high noise levels,the reliability of the system may be increased using techniques such asmodulation, coding, or assigning an SNR margin. SNR margin is theadditional SNR available for a communication channel after modulatingthe carrier with a data signal. For example, if a channel has a SNR of15 dB, but is allotted 10 dB of data, the additional 5 dB is referred toas SNR margin or SNRM. SNR margin is a measure of a communicationssystem's immunity to noise. Increasing the amount of data, whilemaintaining the same bandwidth results in a smaller SNR margin. As aresult, the system can tolerate less noise before bit errors begin tooccur.

SNR margin is used to mitigate the effects of crosstalk and other signalimpairments that occur during transmission. SNR margin may be used, forexample, for noise mitigation in multi-carrier systems, such asAsymmetric Digital Subscriber Line (ADSL) or Very high speed DigitalSubscriber Line (VDSL) systems, which use Discrete Multi-Tone (DMT)modulation. Using SNR margin in a communication system presents atrade-off between data-rate efficiency and noise mitigation. In amulti-carrier system, the allocation of bits on each sub-carrier dependson the SNR available for that sub-carrier. Often, for the sake of linkstability, the total available SNR is not used for bit loading. Instead,only a portion of the SNR is used for bit loading, and the remaining SNRon the sub-carrier is used to mitigate impairments. The unused SNR isthe SNR margin. In one embodiment, 3 dB corresponds to one bit of data.Accordingly, for each 3 dB of SNR margin, one less bit of data is beingtransmitted on that channel.

SUMMARY OF THE INVENTION

Embodiments of the present invention allocate a SNR margin based uponthe data service type assigned to a particular carrier. Embodiments ofthe present invention may allow a system operator to evaluate how muchdata (or how many bits) needs to be modulated, how muchprotection/redundancy is incorporated into the data, and latency limitsfor the data types and, based upon those factors, to allocate SNR marginto individual sub-carriers.

For example, according to an embodiment, a system may transmit one ormore data types, such as voice data and Internet browser data, over asingle physical connection. The data is assigned to separate carriers onthe physical connection. The desired or acceptable latency for the datavaries depending upon the data type. Latency for voice data may beminimized so that delays are not apparent to the user, but latency forInternet browser data is less critical and less apparent to the user.The acceptable error rates may also vary depending upon the dataservice. Errors in voice data will often allow the user to still receivethe message, whereas errors in Internet browser data may cause acomplete failure of a message. The amount of data protection assigned todifferent data types may vary which will affect the amount of data to betransferred. The addition of data protection or redundant bits, such asReed Solomon coding or interleaving, correspondingly reduces the needfor SNR margin. The reduced SNR margin can be used to transmit more dataon the channel. For example, if the SNR margin was reduced by 6 dB on achannel, then two more bits of data, such as error protection data,could be transmitted on that channel.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates bits and SNR margin assigned to tones in amulti-carrier communication system;

FIG. 2 illustrates bits and SNR margin assigned to tones in amulti-carrier communication system according to embodiments of thepresent invention;

FIG. 3 illustrates bits and SNR margin assigned to tones in amulti-carrier communication system;

FIG. 4 illustrates bits and SNR margin assigned to tones in amulti-carrier communication system according to embodiments of thepresent invention;

FIG. 5 illustrates bits and SNR margin assigned to tones in amulti-carrier communication system;

FIG. 6 illustrates bits and SNR margin assigned to tones in amulti-carrier communication system according to another embodiment ofthe invention;

FIG. 7 is a flowchart illustrating a method of using one embodiment ofthe present invention; and

FIG. 8 is a block diagram of a system incorporating one embodiment ofthe invention for assigning SNR margin to carriers.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention. Thepresent invention is be described below with respect to embodiments inexemplary systems, such as an ADSL or VDSL communication system. Theinvention may also be applied, however, to any other wireline orwireless multi-carrier communication system.

Many transmission techniques, including DSL communications systems, havethe capability to transfer multiple types of services, such as voice ordata services, on the same physical medium. For example, a VDSL or ADSLsystem may transmit voice information over the same physical medium,such as a pair of copper wires, that are also used to transmit Internetdata. The different services transmitted in the communication systemtypically have different data rate requirements, different latencyrequirements, different traffic types, and/or different Bit Error Rate(BER) requirements. Although the service requirements for various datatypes are different, the same physical medium is used for all of thedata types and existing systems assign a single SNR margin to all datatypes on the physical medium. Such a constraint causes inefficient useof bandwidth. Different services prioritize different parameters. Forexample, one service may prioritize data rate over latency, whileanother may prioritize BER over latency.

When two data services have different or opposing requirements, such asone service requiring low latency but accepting a high BER, and anotherservice accepting high latency but requiring a very low bit error rate,it is inefficient to use the same noise mitigation parameters for theboth services. Using the same SNR margin for both services often leadsto suboptimal performance for one or both of the services. For channelswith high stationary or fluctuating non-impulsive type noise and lessimpulse noise, using techniques such as trellis coding, SNR margin canimprove the system performance. Whereas, interleaving and Reed Solomon(RS) coding provide limited improvement in quality of service at best onthe same channel. In a channel with high impulse noise and lowfluctuating noise, interleaving in combination with Reed Solomon codingimproves the channel quality, but SNR margin provides little benefit.

Embodiments of the present invention use different SNR margins fordifferent types of services. The amount of protection given to eachservice can be customized based on the requirements of that service. Forexample, in DSL systems, services can be classified in different latencypaths. Latency paths in DSL transmission, such as in ADSL (ITU G.992.1,992.2, 992.3, 992.4, 992.5) and VDSL (ITU G.993.1, 993.2) systems, arespecified based on the delay for each path, data rate, Reed Solomon andnoise protection. Embodiments of the present invention use different SNRmargins for different types of services. This technique can also beapplied to include different SNR margins for different transmissionbands in a composite band plan, different SNR margins for differentparts of the same transmission band, or different SNR margins persub-carrier. Embodiments of the present invention provide a customizablenoise margin for each type of service to ensure that the availablebandwidth is not wasted.

FIG. 1 illustrates a distribution of carriers where the data service isallocated according to a “natural” tone ordering. That is, a first dataservice is assigned to a first group of carriers with lower frequencyn=0 to n=9. Each of signals 101 is assigned the same SNR margin 102.Signals 103 associated with a second data service are assigned to asecond group of carriers with higher frequency. Signals 103 are alsoassigned SNR margin 102, because, in existing systems, all of thesignals on the same physical medium are assigned the same SNR margin.Signals 101 may correspond to a data service having a first latency, afirst BER, a first data rate, or a first traffic type; and signals 103may correspond to a data service having a second latency, a second BER,a second data rate, or a second traffic type.

FIG. 2 illustrates the distribution of data signals according to anembodiment of the present corresponding to FIG. 1 with “natural” toneordering. Signals 201 and 203 represent data signals distributed amongsub-carriers or tones on a physical medium. Signals 201 are allocatedSNR margin 202, which is selected based upon the latency, BER, datarate, or traffic type of the service being transmitted on carriers n ton+9. On the other hand, signals 203 are allocated SNR margin 204, whichis selected based upon the latency, BER, data rate, or traffic type ofthe service being transmitted on carriers n+10 to n+19.

Signals 201 correspond to a data service having a first latency, a firstBER, a first data rate, or a first traffic type; and signals 203correspond to a data service having a second latency, a second BER, asecond data rate, or a second traffic type. SNR margin 204 may be lessthan SNR margin 202, for example, if the service type of signals 203does not require as much SNR margin as the service type of signals 201.For example, signals 201 may provide a low latency at the cost of BER ordata rate, whereas signals 203 may provide better BER or data rate atthe expense of latency. In one embodiment, signals 201 correspond tovoice signals that require low latency, and signals 203 correspond towebpage data that requires a low BER and high data rate. Accordingly,larger SNR margin 202 is appropriate for the voice service, and smallerSNR margin 204 is appropriate for the data service. By optimizing theSNR margin assigned to different services, the available bandwidth isused more efficiently.

In one embodiment, this technique may be applied in a DSL communicationsystem in which data bits for different latency paths are distributedover several sub-carriers in a certain order. For example, in the ADSL1(ITU-G.992.1) and VDSL1 (ITU-TG.993.1) standards, the data bits for“fast-path” services are assigned first, beginning with the tones havingthe lowest bit allocation. Then data for “interleaved-path” services aredistributed to tones with higher bit allocations. For example, referringto FIG. 3, fast-path services are assigned to tones 301, whichcorrespond to the tones or sub-carriers on a physical medium that havethe lowest bit allocations. Then, interleaved-path services are assignedto tones 302, which have higher bit allocations.

The ADSL1 and VDSL1 standards apply a tone-reordering mechanism thatdefines the sequence of carriers in which the data bits are modulated,starting with fast-path data first and followed by interleaved-pathdata. In existing systems, only one SNR margin 303 is available for useby both of these latency paths. Accordingly, all tones 301 and 302 areassigned SNR margin 303. The application of an SNR margin is useful forfast-path services, which do not include much interleaving or RS coding;however, for interleaved-path services, data protection is primarilydependent on interleaving and RS coding. As a result, the use of SNRmargin for interleaved-path services is less than optimal.

FIG. 3 illustrates a distribution of data signals among sub-carriers ortones on a physical medium. FIG. 3 may represent, for example, the SNRmargin allocation for ADSL1- and VDSL1-based systems. Signals associatedwith a first data service are allocated to a first group of tones orsub-carriers 301 that have a lower number of bits assigned. Each of thesignals are assigned the same SNR margin 303. Signals associated with asecond data service are allocated to a second group of tones orsub-carriers 302 that have a higher number of bits assigned. Tones 302are also assigned SNR margin 303, because, in existing systems, all ofthe signals on the same physical medium are assigned the same SNRmargin. Signals 301 may correspond to a data service having a firstlatency, a first BER, a first data rate, or a first traffic type; andsignals 302 may correspond to a data service having a second latency, asecond BER, a second data rate, or a second traffic type. SNR margin 303may be appropriate for signals 301, if signals 301 benefit from SNRmargin protection. However, SNR margin 303 may not be appropriate forsignals 302, if signals 302 are already protected by RS coding or somedata redundancy. In such a scenario, the use of SNR margin 303 withsignals 302 is a waste of bandwidth that could otherwise carry usefuldata.

Instead of splitting the available SNR between data bits and SNR margin,impulse noise protection may be available by using RS or other encoding,which would allow for reduced SNR margin. FIG. 4 illustrates anembodiment wherein a variable SNR margin is assigned to signals in, forexample, an ADSL1 or VDSL1 system. As illustrated in FIG. 4, carriers401 of the first group have a lower bit loading and are assigned to afirst service type having a first SNR margin 403. Carriers 402 of asecond group having higher bit loading are assigned to a second servicetype having second SNR margin 404 that is different from first SNRmargin 403. In one embodiment, the data carried by the service assignedto tones 402 uses data protection, such as RS coding or interleaving,and, therefore, has less need for SNR margin. Accordingly, tones 402 areassigned a smaller SNR margin 404. On the other hand, the data carriedby the service assigned to tones 401 does not have additional dataprojection and, therefore, a larger SNR margin 403 is allocated to thosetones.

FIG. 5 illustrates signals of a known system, which may for example be aADSL2/VDSL2 system, distributed among sub-carriers n to n+19, which areon the same physical medium. Unlike the tone assignment illustrated inFIG. 1 a, the data bits in FIG. 5 are distributed over the tones by atone-ordering algorithm which may for example be determined by areceiver. Tones having data bits of a first latency 501 are interleavedwith tones having data bits of a second latency 502. Accordingly, tonescarrying consecutive bits for a data service or latency path may bespread across the entire available bandwidth on the physical medium. Inthe existing systems, all of the tones are assigned the same SNR margin503 without regard to the data service or latency path of the underlyingdata.

Embodiments of the present invention are effective to improve suchsystems by allowing the system to assign SNR margin based on the dataservice or latency path associated with sub-carriers, even when thesub-carriers carrying bits for the same service are spread out acrossthe spectrum. Embodiments of the present invention provide a techniqueto customize SNR margin for a service channel (i.e. latency/bearerchannel) based on the service requirements of the data carried on thechannel. Embodiments of the invention allow for band-specific anddata-service-specific SNR margin allocation.

FIG. 6 illustrates the SNR margin allocation for an ADSL2/VDSL2 systemaccording to one embodiment of the invention. Signals in an ADSL2/VDSL2system are distributed among sub-carriers n to n+19 on the same physicalmedium. The data bits are distributed over the sub-carriers or tonesusing a tone-ordering algorithm. Tones having data bits of a firstlatency 601 are interleaved with tones having data bits of a secondlatency 603. Tones carrying consecutive bits for a data service orlatency path are spread across the entire available bandwidth on thephysical medium. According to embodiments of the present invention, thetones are assigned an SNR margin based upon the underlying service orlatency path. Signals assigned to latency path 601 are allocated SNRmargin 602, and signals assigned to latency path 603 are allocated SNRmargin 604. Like the SNR margin allocation of FIG. 2, the allocation inFIG. 6 allows the communication system or service provider to evaluatethe trade-offs between allocating excess SNR margin and using availablebandwidth to send data.

According to an embodiment, the embodiments described in FIGS. 4 and 6may use trellis-coded modulation. For example, in systems using4-dimensional trellis-coded modulation, two tones are be provided to thetrellis coder at the same. The Viterbi decoder would equalize the SNRmargin for the tone pairs. It is possible that the tones paired forinput to the trellis coder may be assigned to two different servicesand, therefore, two different SNR margin allocations. This will lead toa condition in which the SNR margins for the different tones areequalized by the Viterbi decoder. In order to avoid such a condition,the following two solutions are proposed.

According to one embodiment, a separate trellis encoder may be used forevery group of tone sets assigned to a particular SNR margin. By doingso, only tones carrying the same SNR margin are paired together andprovided to a respective encoder, therefore, the SNR margins are notchanged.

In another embodiment, tones having the same SNR margin are encoded inbatches using the same encoder. For example, if two SNR margins arespecified, tones carrying data with the first SNR margin will be encodedtogether first, followed by the tones carrying the second SNR margin. Inthis way, the trellis pair will contain tones having the same SNRmargin. According to one embodiment, the tones which are encoded firstmay be carrying the higher SNR margin of the two SNR margins. Accordingto another embodiment, the tones which are encoded first may be carryingthe lower SNR margin of the two SNR margins. It is to be noted that inthe embodiment described with respect to FIG. 6, a reordering of thetones is performed in order to provide the tones of the first groupassigned to a first SNR margin sequentially to the trellis encoder andthereafter the tones of the second group assigned to the second SNRmargin sequentially to the trellis encoder.

Since the tones are provided in pairs to the encoder, there is apossibility that there could be at least one tone pair containing tonesfrom two different SNR margins. This would occur if there were an oddnumber of tones assigned to each SNR margin. In this case, according toone embodiment, the one tone pair containing different SNR margins maybe maintained without adapting SNR margins. According to a furtherembodiment, the one tone pair containing different SNR margins may beadapted to have the same SNR margin, either the smaller or the higherone of the different SNR margins.

FIG. 7 is a flowchart illustrating a method of implementing embodimentsof the present invention in a multi-carrier communication system. Firstthe system identifies first and second data services that aretransmitted in the multi-carrier system (701, 702). Then the systemdetermines a data rate, latency, traffic type, and/or bit error raterequirement for the first and second data services (703, 704). It isexpected that these parameters will vary for the two different dataservices and that the SNR requirements of each data service will bedifferent. The system, then assigns a first SNR margin to the carriersassigned to transmit the first data service and a second SNR margin tothe carriers assigned to transmit the second data service (705, 706).The carriers may be assigned in any manner appropriate for thecommunication system, such as by grouping the carriers for each dataservice together (e.g. FIG. 4) or by interleaving carriers for each dataservice (e.g. FIG. 6). The system then transmits the first and seconddata service so that carriers having the first data service use thefirst signal-to-noise margin, and carriers having the second dataservice use the second signal-to-noise margin (707, 708).

FIG. 8 is a block diagram of a system incorporating one embodiment ofthe present invention. Data terminal 801 communicates with data network802 using a first data service. Voice terminal 803 communicates withvoice network 804 using a second data service. Transceiver 805 receivesdata from data terminal 801 and transmits it to transceiver 806, whichroutes the data to network 802. Transceiver 806 receives data fromnetwork 802 and forwards the data to transceiver 805, which routes thedata to terminal 801. Similarly, transceiver 805 and 806 facilitate theexchange of data between voice terminal 803 and voice network 804.Transceivers 805 and 806 may be comprised of splitters, filters,modulators, demodulators, and processors as is known to those ofordinary skill in the art. For example, network 800 may be an ADSL orVDSL network, and transceivers 805 and 806 may be ADSL or VDSLtransceivers.

Transceiver 805 assigns data from data terminal 801 to a first set ofcarriers on communication link 807, which may be subsequent ornon-subsequent carriers. Transceiver 805 assigns data from voiceterminal 803 to a second set of carrier on communication link 807.Transceiver 805 maintains a first SNR margin for the first set ofcarrier frequencies, wherein the first SNR margin is selected based uponcharacteristics of the first data service from data terminal 801.Transceiver 805 maintains a second SNR margin for the second set ofcarrier frequencies, wherein the second SNR margin is selected basedupon characteristics of the second data service from data terminal 801.The characteristics of the data service may include a data rate, alatency requirement, a traffic type, or a bit error rate limitationimpulse noise protection, retransmission techniques etc. The first setof carrier frequencies and the second set of carrier frequencies may beseparated into separate groups or may be interleaved on link 807.Transceiver 806 also maintains different SNR margins for data being sentfrom networks 802 and 804 to transceiver 805. The SNR margin for a dataservice sent from transceiver 805 to transceiver 806 may be differentthan the SNR margins used for the same data service when sent fromtransceiver 806 to transceiver 805.

Those of ordinary skill in the art will understand that the presentinvention may also be applied to systems that are transmitting more thantwo forms of data across a physical connection and to any data typesthat are being transmitted, including, without limitation, voice, sound,video, photos, multimedia, HTML, text, or telemetry data or the like.Thus, while the exemplary embodiments used herein describe an assignmentof two SNR margins to carriers or tones, it is to be understood that inother embodiments more than two different SNR margins may be assigned tothe available carriers or tones.

Although the exemplary embodiments used herein relate to ADSL or VDSLsystems, it will be understood by those of ordinary skill in the artthat the SNR margin techniques disclosed herein may be applied to anywireline or wireless multi-carrier communication system. The termscarrier, sub-carrier and tone as used herein will be understood to beinterchangeable and to refer to sub-divisions of a communication channelon a wireline or wireless communication link.

Although embodiments of the present invention and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or seeps.

1. A method for assigning signal-to-noise ratio (SNR) margins tocarriers in a multi-carrier system, comprising: assigning a first SNRmargin to a first data service based upon a first servicecharacteristic; assigning a second SNR margin to a second data servicebased upon a second service characteristic; modulating the first andsecond groups of carriers, wherein carriers of the first group ofcarriers are modulated, and thereafter carriers of the second group ofcarriers are modulated; transmitting data associated with the first dataservice on the first group of carriers using the first signal-to-noisemargin; and transmitting data associated with the second data service onthe second group of carriers using the second signal-to-noise margin. 2.The method of claim 1, wherein the first and second servicecharacteristics are selected from the group consisting of: a data rate;a latency requirement; a traffic type; impulse noise protection;retransmission techniques and a bit error rate requirement.
 3. Themethod of claim 1, wherein the first group of carriers and the secondgroup of carriers are transmitted on the same physical medium.
 4. Themethod of claim 3, wherein the physical medium is a wireline connection.5. The method of claim 3, wherein the physical medium is a wirelessconnection.
 6. The method of claim 3, wherein the first group ofcarriers are assigned to a first set of sequential frequencies, and thesecond group of carriers are assigned to a second set of sequentialfrequencies.
 7. The method of claim 3, wherein the first group ofcarriers and the second group of carriers are assigned to non-subsequentfrequencies.
 8. The method of claim 3, wherein the first and secondgroups of carriers are modulated using a trellis coder.
 9. The method ofclaim 8, wherein the first signal-to-noise margin is higher than thesecond signal-to-noise margin.
 10. The method according to claim 8,wherein the first group of carriers and the second group of carriers areassigned to non-subsequent frequencies and wherein the carriers arereordered for trellis code modulation.
 11. The method of claim 1,further comprising: identifying a third data service being transmittedin the multi-carrier system; determining a third service characteristicfor the third data service; assigning a third SNR margin to the thirddata service based upon the third service characteristic; andtransmitting the third data service using the third signal-to-noisemargin.
 12. The method of claim 1, wherein the multi-carrier system isan Asymmetric Digital Subscriber Line (ADSL) system or a Very high speedDigital Subscriber Line (VDSL) system.
 13. A method for allocatingsignal-to-noise (SNR) margin, comprising: identifying a first dataservice being transmitted in a multi-carrier system; identifying asecond data service being transmitted in the multi-carrier system;determining a first service characteristic for the first data service;determining a second service characteristic for the second data service;assigning a first SNR margin to the first data service based upon thefirst service characteristic; assigning a second SNR margin to thesecond data service based upon the second service characteristic;modulating a first and second groups of carriers, wherein carriers ofthe first group of carriers are modulated, and thereafter carriers ofthe second group of carriers are modulated; transmitting the first dataservice on the first group of carriers using the first signal-to-noisemargin; and transmitting the second data service on the second group ofcarriers using the second signal-to-noise margin.
 14. The method ofclaim 13, wherein the first and second service characteristics areselected from the group consisting of: a data rate; a latencyrequirement; a traffic type; and a bit error rate requirement.
 15. Themethod of claim 13, wherein the first group of carriers and the secondgroup of carriers are transmitted on the same physical medium.
 16. Themethod of claim 13, wherein the first group of carriers are assigned toa first set of sequential frequencies, and the second group of carriersare assigned to a second set of sequential frequencies.
 17. The methodof claim 13, wherein the first group of carriers and the second group ofcarriers are assigned to non-subsequent frequencies.
 18. A transceiverfor transmitting data in a multi-carrier system, comprising: a firstapparatus to assign a first SNR margin to a first data service basedupon a first service characteristic; a second apparatus to assign asecond SNR margin to a second data service based upon a second servicecharacteristic; a modulator to modulate a first group of carriers and asecond group of carriers, wherein carriers of the first group ofcarriers are modulated, and thereafter carriers of the second group ofcarriers are modulated; and a transmitter to transmit, to a remotetransceiver, data complying with the first data service on the firstgroup of carriers using the first signal-to-noise margin and totransmit, to the remote transceiver, and data complying with the seconddata service on the second group of carriers using the secondsignal-to-noise margin.
 19. The transceiver of claim 18, furthercomprising: a receiver to receive, from the remote transceiver, datacomplying with the first data service, wherein the received data isassigned a third SNR margin.
 20. The transceiver of claim 18, whereinthe multi-carrier system is an Asymmetric Digital Subscriber Line (ADSL)system or a Very high speed Digital Subscriber Line (VDSL) system. 21.The transceiver of claim 18, wherein the first and second servicecharacteristics are selected from the group consisting of: a data rate;a latency requirement; a traffic type; and a bit error rate requirement.